openrisc: uaccess: Use static inline function in access_ok

As suggested by Linus when reviewing commit 9cb2feb4
("arch/openrisc: Fix issues with access_ok()") last year; making
__range_ok an inline function also fixes the used twice issue that the
commit was fixing.  I agree it's a good cleanup.  This patch addresses
that as I am currently working on the access_ok macro to fixup sparse
annotations in OpenRISC.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Stafford Horne <shorne@gmail.com>
Reviewed-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>